In digital data processing systems, information is frequently stored on magnetic media such as tapes and discs. The recording of digital signals on such media and their recovery is complicated by the fact that magnetic recording systems operate only upon variations in magnetic fields. These variations are a combination of both relative motion between the medium and a read/write head and time-varying signals either fed to or detected by the head. Specifically, such systems typically utilize reversals in magnetic flux patterns in order to record information. As this technique is well known in the magnetic recording and data processing industries, it is unnecessary to further elaborate here. However, it is to be noted that the significance of such technique is that the recovery of the recorded information requires the detection of AC signals and, more precisely, the detection of the peaks of such signals.
According to most, if not all, conventional recording schemes, these AC signals represent the derivatives of the recorded bit streams. Therefore, the maxima and minima (i.e., peaks) indicate the boundaries or transition points between the recorded bits. Consequently, to reconstruct the recorded signal, it is necessary to detect accurately the existence and position of such peaks. However, it is not a simple matter to detect accurately the presence and position of a peak. The design of circuits for peak detectors is complicated by the very large amplitude variations inherent in the recorded and detected signals and the inherent frequency variations involved. For example, phase encoded or "double frequency" recordings contain a two-to-one range in the frequency variations of write head current. In the presence of these conditions, the accurate recovery of data in the presence of noise (either generated by the device mechanism itself or by other sources) becomes one of the most critical and important tasks in designing any magnetic recording systems. Most common peak detector circuits suffer from problems related to sensitivity to phase shifts and noise.